docs: def integral(self, bandname):
          """Calculate the integral of the spectral response function for each
          detector.
          """
          intg = {}
          for det in self.rsr[bandname].keys():
              wvl = self.rsr[bandname][det]['wavelength']
              resp = self.rsr[bandname][det]['response']
              intg[det] = np.trapz(resp, wvl)
          return intg